1. Field of the Invention
The present invention relates to wireless integrated circuit (IC) devices. More particularly, the present invention relates to a wireless IC device used in a radio frequency identification (RFID) system and a wireless IC device composite component used in the wireless IC device.
2. Description of the Related Art
Recently, RFID systems have been developed as management systems of articles. In a typical RFID system, a reader-writer that generates an induction field communicates with a wireless tag (hereinafter referred to as a wireless IC device) that is attached to an article, that stores certain information, and that transmits the information in a non-contact manner.
Wireless IC devices used in the RFID systems are disclosed in, for example, U.S. Pat. No. 6,406,990 and U.S. Pat. No. 6,664,645.
Specifically, a wireless IC device shown in FIG. 32 is disclosed, in which an air-core type antenna pattern 304 made of an aluminum foil, a wireless IC chip 301 directly connected to locations on the antenna pattern 304 via Au bumps 302, and a resin layer 303 arranged so as to cover the Au bumps 302 to ensure the bonding strength of the wireless IC chip 301 are provided on a support film 305 made of polyethylene terephthalate (PET).
In this wireless IC device, the wireless IC chip 301 is directly connected to the antenna pattern 304 via the Au bumps 302 and it is necessary to arrange the wireless IC chip 301 on the support film 305 having an area that is significantly greater than that of the wireless IC chip 301. However, it is very difficult to accurately mount the wireless IC chip 301 on the large support film 305, and there is a problem in that the resonant frequency characteristics of the antenna vary if the wireless IC chip 301 is displaced from a desired location or if the sizes of the Au bumps 302 vary. In addition, since the frequency characteristics of the wireless IC device are substantially determined by the shape or size of the antenna pattern 304, the frequency characteristics are likely to vary if the antenna pattern 304 is curled or is sandwiched between dielectric bodies (for example, the antenna pattern 304 is sandwiched in a book).
Furthermore, the resonant frequency of signals transmitted or received by the wireless IC device is primarily determined by the electrical length of the antenna pattern. For example, when transmission-reception signals within a bandwidth of about 13.5 MHz are processed in the air-core type antenna pattern, the antenna pattern is increased in size because an inductance of about 4.5 μH is required.